1. Field of the Invention
The present invention relates to a reciprocating piston compressor such as a swash plate type compressor. More specifically, the present invention relates to a compressor which can constantly perform appropriate discharging actions irrespective of the compression ratio.
2. Description of the Related Art
Reciprocating piston compressors are generally used for air-conditioning passenger compartments in vehicles. In the typical reciprocating piston compressor, a swash plate is supported on a drive shaft, and the wobbling motion of the swash plate caused by rotation of the drive shaft is converted to reciprocating motion of the pistons. With the reciprocating motion of the pistons, gas is sucked from a suction chamber to each cylinder bore, is compressed, and is discharged to a discharge chamber.
Japanese Unexamined Patent Publication No. Hei 5-79456 discloses such a compressor in which a front housing 100 is fixed to the front end of a cylinder block 101 as shown in FIG. 6. A rear housing 106 is fixed to the rear end of the cylinder block 101 with a valve plate 105 interposed therebetween. A drive shaft 103 is rotatably supported in a supporting hole 102 of the cylinder block 101. A swash plate 99, which is fitted on the drive shaft 103, wobbles when the drive shaft 103 is rotated. The cylinder block 101 contains a plurality of cylinder bores 104 formed around the drive shaft 103. A piston 108 is located in each cylinder bore 104 and connected via a piston rod 98 to the swash plate 99.
A suction chamber 107 and a discharge chamber 109 are formed in the rear housing 106. Discharge ports 110, which are formed in the valve plate 105, allow the cylinder bores 104 to communicate with the discharge chamber 109. A flapper type discharge valve 111 and a retainer 112 are applied to the valve plate 105 on the discharge chamber (109) side in association with the corresponding discharge port 110. The discharge valve 111 opens or closes the associated discharge port 110 depending on the difference between the pressure in the cylinder bore 104 and the pressure in the discharge chamber 109 (hereinafter referred to as the discharge pressure). The retainer 112 regulates the aperture of the discharge valve 111.
A communication passage 113 is formed between the supporting hole 102 and each cylinder bore 104. A rotary valve 114, which is contained in the supporting hole 102, is connected to the rear end of the drive shaft 103 to be rotatable integrally therewith. The rotary valve 114 contains a suction passage 115 and a discharge passage 116.
Wobbling of the swash plate 99 caused by the rotation of the drive shaft 103 is transmitted to pistons 108 via the piston rods 98 to allow the pistons 108 to reciprocate in the cylinder bores 104. Suction of a refrigerant gas into the cylinder bores 104, compression of the refrigerant gas in the cylinder bores 104 and discharge of the compressed gas are achieved by the reciprocating motion of the pistons 108.
More specifically, with the rotation of the rotary valve 114 in synchronization with the drive shaft 103, communication is established between the communication passages 113 of the respective cylinder bores 104 in which the piston 108 is in the suction stroke and the suction chamber 107 via the suction passage 115 of the rotary valve 114 for a predetermined time. Thus, the refrigerant gas in the suction chamber 107 is sucked into the cylinder bores 104 sequentially. Further, after the refrigerant gas is compressed by the pistons 108, communication is established for a predetermined time, via the discharge passage 116 of the rotary valve 114, between the discharge chamber 109 and the communicating passage 113 of the cylinder bore 104 in which the piston 108 is in a predetermined discharge stroke at a certain time. It should be noted here that the certain time is when the pressure in the cylinder bore 104 reaches a predetermined value. This value corresponds to the pressure required in the cylinder bore 104 when the compressor is driven at a high compression ratio, i.e., the discharge pressure when the compressor is driven at a high compression ratio.
For example, when the discharge pressure is high and the compressor is driven at a high compression ratio, the communication between the cylinder bore 104 and the discharge chamber 109 is established after the pressure in the cylinder bore 104 is substantially equilibrated with the high discharge pressure, and thus the refrigerant gas in the cylinder bore 104 can securely be discharged to the discharge chamber 109. Therefore, in this compressor, the cylinder bore 104 does not communicate with the discharge chamber 109 before the pressure in the cylinder bore 104 is sufficiently increased so that the refrigerant gas does not flow back from the discharge chamber 109 into the cylinder bore 104.
When the discharge pressure is low and the compressor is driven at a low compression ratio, the discharge valve 111 opens when the pressure in the cylinder bore 104 becomes slightly higher than the discharge pressure, and the refrigerant gas in the cylinder bore 104 is discharged through the discharge port 110 to the discharge chamber 109. In other words, in the situation where the pressure in the cylinder bore 104 greatly exceeds the discharge pressure before communication is established between the communication passage 113 and the discharge chamber 109 via the discharge passage 116, the discharge valve 111 opens to prevent the pressure in the cylinder bore 104 from increasing unnecessarily. Accordingly, the compressor does not perform useless compressing actions to cause pressure loss.
As described above, when the above compressor is driven at a high compression ratio, the refrigerant gas is discharged through the discharge passage 116 of the rotary valve 114 which is rotated integrally with the drive shaft 103. Accordingly, the rotary valve is free from the problems of noise and fatigue, typical in flapper type valves, caused by the opening and closing of the valve. Further, when the compressor is driven at a low compression ratio, the refrigerant gas is discharged through the flapper type discharge valve 111, which opens depending on the difference between the pressure in the cylinder bore 104 and the discharge pressure. Accordingly, pressure loss, which is caused when the refrigerant gas is discharged using the rotary valve 114 only, does not occur.
However, in the above-described compressor, one discharge valve 111 is required for each cylinder bore 14. In addition, the valve plate 105 must be placed between the cylinder block 101 and the rear housing 106 so as to position the discharge valves 111. Also, a retainer 112 must be employed for each discharge valve 111. Accordingly, a number of extra parts in addition to the rotary valve 114 are required, which not only adds to the cost but complicates the structure. Consequently, not only are production costs elevated, but assembly becomes laborious and the compressor is enlarged.